Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming
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• Original Paper •
Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming Shuangmei MA and Congwen ZHU* State Key Laboratory of Severe Weather and Institute of Climate System, Chinese Academy of Meteorological Sciences, Beijing 100081, China (Received 17 March 2020; revised 15 July 2020; accepted 14 August 2020) ABSTRACT Under recent Arctic warming, boreal winters have witnessed severe cold surges over both Eurasia and North America, bringing about serious social and economic impacts. Here, we investigated the changes in daily surface air temperature (SAT) variability during the rapid Arctic warming period of 1988/89–2015/16, and found the daily SAT variance, mainly contributed by the sub-seasonal component, shows an increasing and decreasing trend over eastern Eurasia and North America, respectively. Increasing cold extremes (defined as days with daily SAT anomalies below 1.5 standard deviations) dominated the increase of the daily SAT variability over eastern Eurasia, while decreasing cold extremes dominated the decrease of the daily SAT variability over North America. The circulation regime of cold extremes over eastern Eurasia (North America) is characterized by an enhanced high-pressure ridge over the Urals (Alaska) and surface Siberian (Canadian) high. The data analyses and model simulations show the recent strengthening of the high-pressure ridge over the Urals was associated with warming of the Barents–Kara seas in the Arctic region, while the high-pressure ridge over Alaska was influenced by the offset effect of Arctic warming over the East Siberian–Chukchi seas and the Pacific decadal oscillation (PDO)–like sea surface temperature (SST) anomalies over the North Pacific. The transition of the PDO-like SST anomalies from a positive to negative phase cancelled the impact of Arctic warming, reduced the occurrence of extreme cold days, and possibly resulted in the decreasing trend of daily SAT variability in North America. The multi-ensemble simulations of climate models confirmed the regional Arctic warming as the driver of the increasing SAT variance over eastern Eurasia and North America and the overwhelming effect of SST forcing on the decreasing SAT variance over North America. Therefore, the regional response of winter cold extremes at midlatitudes to the Arctic warming could be different due to the distinct impact of decadal SST anomalies. Key words: daily surface air temperature variability, extreme cold days, Arctic warming, eastern Eurasia, North America Citation: Ma, S. M. and C. W. Zhu, 2020: Opposing trends of winter cold extremes over eastern Eurasia and North America under recent Arctic warming. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-020-0070-2. (in press) Article Highlights:
• The regional daily SAT variability shows opposite trends over eastern Eurasia and North America. • Increasing and decreasing cold extremes dominated the increase and decrease of the daily SAT variability over eastern Eurasia and North America, respectiv
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